The present invention relates to a system and method of performing an electrosurgical procedure using an electrosurgical (ablation or electrocautery) device. More particularly, it relates to a method of performing an electrosurgical procedure using an ablation or electrocautery system to create a lesion.
A wide variety of surgical procedures involve ablation or cauterization of selected tissue. For example, hemorrhoid or varicose vein removal can be accomplished by ablating the tissue in question. Additionally, tissue ablation and/or cauterization is commonly employed for the surgical treatment of cardiac arrhythmia and, in particular, atrial fibrillation. In general terms, cardiac arrhythmia relates to disturbances in the heart""s electrical system that causes the heart to beat irregularly, too fast or too slow. Irregular heartbeats, or arrhythmia, are caused by psychological or pathological disturbances in the discharged electrical impulses from the sinoatrial node, and the transmission of the signal through the heart tissue, or spontaneous, unexpected electrical signals generated within the heart. One type of arrhythmia is tachycardia, which is an abnormal rapidity of heart action. There are several different forms of atrial tachycardia, including atrial fibrillation and atrial flutter. With atrial fibrillation, instead of a single beat, numerous electrical impulses are generated by depolarizing tissue at one or more locations in the atria (or possibly other locations). These unexpected electrical impulses produce irregular, often rapid heartbeats in the atrial muscles and ventricles. As to the location of the depolarizing tissue, it is generally agreed that the undesired electrical impulses often originate in the left atrial region of the heart, and in particular in one (or more) of the pulmonary veins extending from the left atrium. With this in mind, and as an alternative to drug therapy, ablation of the abnormal tissue or accessory pathway responsible for the atrial fibrillation has proven highly viable.
Regardless of exact application, ablation or cauterization of tissue is typically achieved by applying a destructive energy source to the target tissue, including radiofrequency electrical energy, direct current electrical energy, and the like. The ablative energy source is provided by an electrode and is otherwise placed in contact with the target tissue. The electrode can be formed as part of a handheld electrosurgical instrument. As used herein, the term xe2x80x9celectrosurgical instrumentxe2x80x9d includes a handheld instrument capable of ablating or cauterizing tissue. The instrument rigidly couples the electrode tip to an instrument handle that is otherwise held and manipulated by the surgeon. The rigid construction of the electrosurgical instrument typically requires direct, open access to the target tissue. Thus, for treatment of atrial fibrillation via an electrosurgical instrument, it is desirable to gain access to the patient""s heart through one or more openings in the patient""s chest (such as a sternotomy, a thoractomy, a small incision and/or a port). In addition, the patient""s heart may be opened through one or more incisions, thereby allowing access to the endocardial surface of the heart.
Once the target site (e.g., right atrium, left atrium, endocardial surface, epicardial surface, etc.) is accessible, the surgeon positions the electrode tip of the electrosurgical instrument at the target site. The tip is then energized, ablating (or for some applications, cauterizing) the contacted tissue. A desired lesion pattern is then created (e.g., portions of a known xe2x80x9cMazexe2x80x9d procedure) and moving the tip in a desired fashion along the target site. In this regard, the surgeon can easily control positioning and movement of the tip, as the electrosurgical instrument is rigidly constructed and relatively short.
Electrosurgical instruments, especially those used for treatment of atial fibrillation, have evolved to include additional features that provide improved results for particular procedures. For example, U.S. Pat. No. 5,897,553, the teachings of which are incorporated herein by reference, describes a fluid-assisted electrosurgical instrument that delivers a conductive solution to the target site in conjunction with electrical energy, thereby creating a xe2x80x9cvirtualxe2x80x9d electrode. The virtual electrode technique has proven highly effective at achieving the desired ablation while minimizing collateral tissue damage. Other electrosurgical instrument advancements have likewise optimized system performance. Unfortunately, however, use of the electrosurgical instrument to produce a lesion having desired characteristics has remained a lengthy and intense procedure.
Typically, a lesion is created by repeatedly drawing the electrosurgical instrument across the target tissue site. Before, during, and after each pass of the electrosurgical instrument across the target tissue site, the tissue is carefully monitored and tested to determine the depth of lesion penetration on the target tissue site. Monitoring and testing of the site ensure the proper number of passes of the electrosurgical instrument to create a lesion having the desired depth for a particular procedure.
Although creating a lesion by repeatedly drawing the electrosurgical instrument across a target tissue site is an effective method, the need for constant monitoring and testing increases the length of time required to perform the procedure. Overall procedure time is critical to the safety of the surgery. For example, a prolonged surgical treatment for atrial fibrillation increases the length of time the heart is stopped and opened and, consequently, increases the chance of complication and infection. As a result, advancements are needed to decrease the time of such electrosurgical procedures.
Electrosurgical procedures utilizing electrosurgical instruments remain a viable method of lesion production for a variety of surgical treatments, including the surgical treatment of atrial fibrillation. However, typical procedures require prolonged operation time due to the need for constant testing and monitoring of the tissue and lesion depth. Therefore, a need exists for an electrosurgical procedure that reduces reliance upon testing and monitoring during the procedure, and thereby reduces procedure time and the risk of complication.
One aspect of the present invention relates to a method of making a lesion on living tissue at a target site. The method includes providing an electrosurgical system, determining a desired lesion depth, selecting a desired power setting, and applying electrical energy to the living tissue. The electrosurgical system includes an electrosurgical instrument having an electrode at a distal portion thereof, and a power source having multiple available power settings. The power source is electrically connected to the electrode. The step of applying electrical energy includes energizing the electrode, via the power source, at the selected power setting for a recommended energization time period that is determined by reference to predetermined length of time information and based upon the desired lesion depth and the selected power setting. In one preferred embodiment, the predetermined length of time information is embodied in a look-up table. In another preferred embodiment, the electrosurgical system further includes a fluid source maintaining a supply of fluid. The fluid source is fluidly connected to the electrosurgical instrument and is configured to irrigate the electrode at an irrigation rate. In this regard, the predetermined length of time information is generated as a function of irrigation rate.
Another aspect of the present invention relates to an electrosurgical system for performing an electrosurgical procedure on living tissue. The electrosurgical system includes an electrosurgical instrument having an electrode at a distal portion thereof, a power source having multiple available power settings, and an energization look-up table. The power source is electrically connected to the electrosurgical instrument for selectively energizing the electrode. The energization look-up table includes a power setting data set, a lesion depth data set, and a corresponding energization time period information that is organized as a function of the power setting and lesion depth data sets. The energization time period information is adapted to identify a recommended energization time period for a particular electrosurgical procedure based upon a cross-reference of a desired power setting relative to the power setting data set and a desired lesion depth relative to the lesion depth data set.